A) Field of the Invention
The present invention relates to an optical device, and more particularly to an optical device whose optical transmission characteristics are changed by changing a photonic band structure by applying an external field to photonic crystals.
B) Description of the Related Art
In photonic crystals, in which mediums having a different refractive index from that of a background medium are periodically arranged in the background medium, it is known that a photonic band structure for electromagnetic waves different from usual optical crystals is generated. In the photonic crystals, existence of a frequency band called a photonic band gap inhibiting optical transmission has been reported (E. Yablonovitch, Physical Review Letters, Vol. 58, No. 20, pp. 2059 to 2062, The American Physical Society (1987)), and revelation of large optical deflection called a super prism effect has been reported (H. Kosaka, et al., Physical Review B Vol. 58, No. 16, R10 096, The American Physical Society (1998)). The photonic crystals having such properties are expected as core technologies for making compact optical devices.
Description will be made on an optical device utilizing photonic crystals disclosed in JP-A-2002-333602. In a background optical medium whose refractive index will not change, an optical medium having a variable refractive index is periodically distributed to form photonic crystals. As an electric field is applied to the photonic crystals, the refractive index of the periodically distributed optical medium changes. The photonic band structure changes therefore to change the optical transmission characteristics.